The use of chip carriers for packaging of silicon integrated circuits is the subject of increasing interest in the industry. Typically, a semiconductor chip is bonded to, and sealed within, the chip carrier. Electrically conductive paths connect to the chip, pass through the wall of the carrier and terminate on the bottom thereof as bonding pads or leads. The chip carrier is typically surface bonded to contact pads on a supporting substrate which can be a printed wiring board, a ceramic substrate or the like, including a thick film or thin film circuit.
A convenient method of bonding is by soldering together corresponding contact pads on the carrier and substrate. Solder can be applied to the contact pads by dipping or the like. However, reliable connections usually require a precise solder volume per connection which is not easily obtainable by such methods. In addition, a relatively large gap between the bottom of the carrier and the surface of the substrate is usually required to permit cleaning and encapsulation.
It is well known to bond a chip carrier to the supporting substrate by attaching small spherical solder preforms, often referred to as "solder bumps", to the contact areas of the chip carrier to provide the desired gap. The preforms are then placed in contact with the pads on the supporting substrate and heated to cause the solder to reflow to bond the contact pads to the substrate pads while maintaining a predetermined gap therebetween.
Heretofore, various techniques have been used to handle the small spherical solder bodies. One such technique, described in U.S. Pat. No. 3,320,658 to F. J. Bolda et al., makes use of a hand held vacuum feeder arm capable of sucking up one spherical body at a time and selectively depositing it at preselected locations on a carrier.
One known handling technique capable of increasing the throughput of the aforementioned handling operation is described in U.S. Pat. No. 4,332,341 to R. H. Minetti. That patent discloses the use of a ram head having a pattern of spherical depressions formed therein with the pattern corresponding to the layout of the contact pads of a chip carrier. The ram head is moved downward into a reservoir of spherical bodies of solder, and vacuum is applied to each one of the spherical depressions thereby positioning a spherical body into each depression. The spherical bodies are heated to a temperature below the melting point of the solder and brought into contact with pads of the chip carrier with sufficient mechanical force to produce a bond while the solder is kept in a solid phase.
Although the above-described known techniques are adequate for their respective purposes, there still exists a need for a technique specifically directed to high volume production of bumped chip carriers.